Harry's GPS Suite Forum

I decided to do a little test run with LapTimer before trying to use it at the track. I made a "track" by putting a POI on a public road in a location where I could do a complete loop without stopping. I mounted the iPhone in portrait orientaition, in close to a vertical plane. I got results, but the longitudinal acceleration values all hover around -1 G. This was normal driving, not racing. (I used my Mitsubishi Delica, to avoid any temptation to drive inappropriately!)

Was I simply not accelerating hard enough for the software to kick into the mode where it measures longitudinal acceleration? It seems as though it was measuring vertical acceleration -- i.e., along the longitudinal axis of the iPhone, not the car. Should I have mounted it horizontally?

Did you start the app while already mounted in the final position or did you start it and then mounted it? You can also calculate the g-fprces from the gps data: go to "Lap Details" and look for the button at the bottom "Recalculate".